Field of the Invention
The present invention relates to a touch detection sensor structure of a touch screen panel for detecting a capacitive type touch input by a human finger or a touch input tool having conductive characteristics similar thereto, and more particularly, to a touch detection method for diversifying a sensor structure installed in a touch screen panel to improve a resolution of coordinates detected upon a detection of a touch signal by making a sensor and a touch input tool opposite to each other.
Discussion of the Background
Generally, a touch screen panel is attached on display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), and an organic light emitting diode (OLED), an active matrix organic light emitting diode (AMOLED) and is one of the input apparatuses that generate signals corresponding to positions where objects such as a finger and a pen are touched. The touch screen panel has been used in wide applications such as small portable terminals, industrial terminals, and digital information devices (DIDs).
Typically, various types of touch screen panels have been disclosed. However, a resistive touch screen panel having simple manufacturing process and low manufacturing costs has been most widely used. However, the resistive touch screen panel has the low transmissivity and needs to be applied with a pressure, For this reason, the resistive touch screen panel is inconvenient to use, has a difficulty in implementing a multi touch and a gesture cognition, leads to a detection error, etc.
On the other hand, a capacitive type touch screen panel may have high transmissivity, cognize a soft touch, and implement better multi touch and gesture cognition. As a result, the capacitive type touch screen panel is gradually expanding into new markets.
FIG. 1 illustrates an example of the existing capacitive type touch screen panel. Referring to FIG. 1, transparent conductive layers are formed on upper and lower surfaces of a transparent substrate 2 made of plastic, glass, etc., and voltage applying metal electrodes 4 are formed at each of the four corners of the transparent substrate 2. The transparent conductive layer is made of transparent metals such as indium tin oxide (ITO) and antimony tin oxide (ATO). Further, the metal electrodes 4 formed at four corners of the transparent conductive layer are formed by being printed with conductive metal having low resistivity such as silver Ag. A resistance network is formed around the metal electrodes 4. The resistance network is formed in a linearization pattern to equally send out a control signal to the whole surface of the transparent conductive layer. Further, an upper portion of the transparent conductive layer including the metal electrode 4 is coated with a passivation layer.
In the capacitive type touch screen panel as described above, a high-frequency alternating voltage is applied to the metal electrode 4 and thus is conducted over the whole surface of the transparent substrate 2. In this case, when the transparent conductive layer on an upper surface of the transparent substrate 2 is light touched with a finger 8 or a conductive touch input tool, a change in current is sensed by a current sensor embedded in a controller 6 while a predetermined amount of current is absorbed into a body and current amounts at each of the four metal electrodes 4 are calculated, thereby cognizing touched points.
However, the capacitive type touch screen panel as illustrated in FIG. 1 is based on a method for detecting a magnitude of micro current. As a result, the capacitive type touch screen panel needs an expensive detection apparatus and therefore a price of the capacitive type touch screen panel goes up and the capacitive type touch screen panel is hard to implement a multi touch for cognizing a plurality of touches.
To overcome the above problems, the capacitive type touch screen panel as illustrated in FIG. 2 has been mainly used in recent years. The touch screen panel of FIG. 2 is configured to include a lateral linear sensor 5a, a longitudinal linear sensor 5b, and a touch drive IC 7 analyzing a touch signal. The touch screen panel is based on a method for detecting a magnitude of capacitance formed between the linear sensor 5 and the finger 8 and scans the lateral linear sensor 5a and the longitudinal linear sensor 5b to detect a signal, thereby cognizing the plurality of touched points.
However, when the above-mentioned touch screen panel is installed on a display device such as an LCD, the touch screen panel is hard to detect a signal due to noise. For example, the LCD uses a common electrode to which alternating common voltage Vcom is applied, in some cases. Further, the common voltage Vcom of the common electrode acts as noise upon detecting the touched point.
FIG. 3 illustrates an embodiment in which the existing capacitive type touch screen panel is installed on the LCD. A display device 200 has a structure in which a liquid crystal is sealed between a TFT substrate 205 at a lower portion thereof and a color filter 215 at an upper portion thereof to form a liquid crystal layer 210. To seal the liquid crystal, the TFT substrate 205 and the color filter 215 are bonded to each other by having a sealant 230 disposed at outer portions thereof. Although not illustrated, polarizing plates are attached to upper and lower portions of a liquid crystal panel and back light units (BLUs) are additionally installed at the liquid crystal panel.
As illustrated, the touch screen panel is installed at the upper portion of the display device 200. The touch screen panel has a structure in which the linear sensor 5 is put on an upper surface of the substrate 1. A protection panel 3 for protecting the linear sensor 5 is attached on the substrate 1. The touch screen panel is bonded to an edge portion of the display device 200 by an adhesive member 9 such as a double adhesive tape (DAT), in which an air gap 9a is formed between the touch screen panel and the display device 200.
In this configuration, when a touch is generated as illustrated in FIG. 3, a capacitance such as Ct is formed between the finger 8 and the linear sensor 5. However, as illustrated, a capacitance such as Cvcom is also formed between the linear sensor 5 and the common electrode 200 formed on a lower surface of the color filter 215 of the display device 200 and an unknown parasitic capacitance Cp that occurs due to a capacitance coupling between patterns, manufacturing process factors, etc., is also applied to the linear sensor 5. Therefore, a circuit like an equivalent circuit of FIG. 4 is configured.
Here, the existing touch screen panel detects a variation of Ct to cognize a touch and Cvcom and Cp act as noise upon detecting the Ct.
Typically, to remove the noise, as illustrated in FIG. 3, an air gap 9a is disposed between the touch screen panel and a display device 200. Further, although not illustrated, a lower surface of the substrate 1 of the touch screen panel is coated with ITO, or the like to form a shielding layer and the shielding layer is grounded to a ground signal.
However, due to the air gap 9a, a thickness of products may be increased and a quality of products may deteriorate. Further, a separate shielding layer and a manufacturing process for forming the shielding layer are required and therefore manufacturing costs may be increased. In particular, when the touch screen panel built in the LCD, the air gap 9a or the shielding layer may not be formed. Therefore, the touch screen panel may not be manufactured to be built in the display devices such as the LCD.
To solve the above problems, the touch detection method as illustrated in FIG. 5 is proposed. Referring to FIG. 5, a sensor of FIG. 5 is not the linear sensor as illustrated in FIG. 2 but is configured of only one sensor 10. The sensor is connected to point P which is a touch detector, and applies a driving voltage through an auxiliary capacitor Caux connected to the point P and when the touch capacitance Ct is applied between the sensor 10 and the touch input tool, uses the phenomenon that a difference in magnitude in voltage or current detected by the touch detector depending on the magnitude in the touch capacitance occurs, thereby detecting a touch signal. The detection method detects noise occurring in the display device such as the LCD and detects the touch signal while avoiding the occurrence timing of the noise to detect the touch signal independent of the noise. Alternatively, since a size of the noise detected by one sensor as illustrated in FIG. 5 is smaller than that of the noise detected by a plurality of interconnected sensors as illustrated in FIG. 2, the touch signal may be detected while being less sensitive to noise in a touch screen panel structure as illustrated in FIG. 6.
FIG. 5 illustrates an embodiment of a configuration of one sensor and the touch screen panel configured of a plurality of sensors is configured as illustrated in FIG. 6. Referring to FIG. 6, a configuration of a touch IC 30 is illustrated at a lower portion of FIG. 6. The touch IC 30 may include a driver 31 including a multiplexer, a touch detector 14, a timing controller 33, a signal processor 35, and a memory unit 28 and may further include a power supply unit 47, a communication unit 46, and a CPU 40.
The touch signal or the touch coordinate detected by the touch IC 30 is transferred to the CPU 40. The CPU 40 may be a CPU of the display device, a main CPU of a computer device, or a CPU of the touch screen panel itself. For example, the CPU may have a 8-bit microprocessor, 16-bit microprocessor, etc., embedded therein to process the touch signal.
The microprocessor embedded in the touch IC 30 may operate the coordinates input by the touch to cognize gestures such as a touch point, a zoom, a rotation, and a move and transfer data such as a reference coordinate (or central point coordinate) and gestures to the main CPU. Further, the microprocessor may process data in various ways such as generating a zooming signal by operating an area of the touch input, calculating strength of the touch input, and cognizing only a user's desired (for example, large-area detected) GUI object as an effective input when a plurality of GUI objects are simultaneously touched and output the processed data.
A timing controller 33 generates a time division signal less than tens of ms and the signal processor 35 transmits and receives signals to and from each sensor 10 through the driver 31. The driver 31 supplies an on/off control signal Vg of a charging means 12 and a precharge signal Vpre. The on/off control signal Vg is time-divided by the timing controller 33 to be sequentially or non-sequentially supplied to each sensor 10. The memory unit 28 is to store an initial value which is a signal when a touch is not generated at each sensor 10 or is to store a signal when a touch is generated and has unique absolute addresses for each sensor 10.
As such, the memory unit 28 may include only one memory means to temporarily store acquired coordinate values or a reference value when the touch is not generated. Alternatively, the memory unit 28 may include a plurality of memory means to separately store the reference value when the touch is not generated and a detection value when the touch is generated.
The embodiment illustrated in FIG. 6 illustrates the case in which sensor 10 has a resolution of 6 rows*5 columns, which is only an embodiment. Actually, the sensor 10 has a higher resolution, that is, has a larger number of sensors in a row and a larger number of sensors in a column. For example, a case in which the sensor has a resolution of 20×20 may be expected.
FIG. 7 is an embodiment of a touch screen panel installed on an upper surface of the display device 200. As illustrated in FIG. 7, the display device 200 has the common electrode 200. An AMOLED does not have a common voltage with a function to display an image quality. However, a virtual potential layer in which the common electrode capacitance Cvcom may be formed is formed between a TFT substrate and the sensor 10, which is also called the common electrode. The display device 200 may be various types of display devices as described above and the common electrode 220 may be a Vcom electrode of the LCD or other types of electrodes. An embodiment of FIG. 10 illustrates an LCD among the display devices.
The display device 200 illustrated in FIG. 7 has a structure in which a liquid crystal is sealed between a TFT substrate 205 at a lower portion and a color filter 215 at an upper portion to form a liquid crystal layer 210. To seal the liquid crystal, the TFT substrate 205 and the color filter 215 are bonded to each other by having a sealant 230 disposed at outer portions thereof. Although not illustrated, a polarizer is attached to the upper and lower portions of the liquid crystal panel. In addition, optical sheets configuring a back light unit (BLU) and a brightness enhancement film (BEF) may be installed like the BLU.
As illustrated, the substrate 50 of the touch screen panel is installed on the display device 200. As illustrated in FIG. 7, the substrate 50 has an outer portion attached on the display device 200 by an adhesive member 57 such as a double adhesive tape (DAT). Further, an air gap 58 is formed between the substrate 50 and the display device 200.
A common voltage level which is a DC alternating at a predetermined frequency and having a varying or constant magnitude is applied to the common electrode 220 of the display device 200. For example, in a small LCD with a line inversion, the common voltage of the common electrode 220 alternates as illustrated in FIG. 5 and in the LCD such as a notebook and a monitor/TV with a dot inversion, the common voltage having a DC level which is a voltage having a predetermined magnitude is applied.
As illustrated, the common electrode capacitance Cvcom is formed between the sensor 10 and the common electrode 220 of the display device 200. If any precharge signal is applied to the sensor 10, the common electrode capacitance Cvcom has a predetermined voltage level by a charging voltage. In this case, one end of the common electrode capacitance Cvcom is grounded to the common electrode 220, such that when the common electrode 220 is an alternating voltage, a potential at the sensor 10 which is the other terminal of the common electrode capacitance Cvcom alternates due to the alternating voltage applied to the common electrode 220 and when the common electrode is a DC, the potential at the sensor 10 does not alternate.
Meanwhile, non-explained reference numeral 24 in the drawings is a passivation layer 24 for protecting the sensor 10.
In the structure, the touch signal is detected at point P of FIG. 5, that is, the touch detector 14 by the following Equations.
                              Δ          ⁢                                          ⁢          Vsensor                =                              ±                          (                              Vh                -                Vl                            )                                ⁢                      Caux                          Caux              +              Cvcom              +              Cp                                                          〈                  Equation          ⁢                                          ⁢          1                〉                                          Δ          ⁢                                          ⁢          Vsensor                =                              ±                          (                              Vh                -                Vl                            )                                ⁢                                          ⁢                      Caux                          Caux              +              Cvcom              +              Cp              +              Ct                                                          〈                  Equation          ⁢                                          ⁢          2                〉            
(In the above Equations, ΔVsensor represents the touch signal detected by the touch detector 14, Vh represents a high level voltage applied to the auxiliary capacitor, V1 represents a low level voltage applied to the auxiliary capacitor, Caux represents an auxiliary capacitor capacitance, Cvcom represents the common electrode capacitance, Cp represents the parasitic capacitance, and Ct represents the touch capacitance.
Referring to the above <Equation 1> and <Equation 2>, the above <Equation 1> represents the touch signal detected by the touch detector 14 when the touch is not made and the above <Equation 2> represents the touch signal detected by the touch detector 14 when the touch is made by a finger, that is, when the finger and the sensor 10 are opposite to each other. The difference between the above <Equation 1> and <Equation 2> is a difference on whether the Ct which is the touch capacitance is present in a denominator. In this case, when the touch capacitance Ct is generated by the touch, amplitude of a signal detected depending on the above <Equation 2> is changed due to the magnitude of the generated touch capacitance Ct. Therefore, it is possible to detect the amplitude of the touch signal by operating the changed signal amplitude.
The touch signal detected by each sensor 10 based on the difference between the above <Equation 1> and <Equation 2> is transferred to the CPU 40 or the signal processor 35 discriminate whether the touched finger (conductor, hereinafter, referred to as an object) is one, two, or more and then operate the touch coordinate. When the object is touched to the sensors 10 a lot farther away from each other, it is not difficult to differentiate the number of touched objects. However, it is difficult to differentiate how many objects are present in a state in which the plurality of objects are touched to one sensor 10 or are touched to adjacent sensors.
FIG. 8 is the existing embodiment for discriminating the number of objects. FIG. 8 illustrates a state in which four (sensor A 801, sensor B 802, sensor C 803, and sensor D 804) sensors 10 are present in one column and a multi-touch (touch 1, touch 2) by two objects is performed.
It is assumed that the touch of the upper portion by any object is called “touch 1” and a touch of the lower portion by any object is called “touch 2”. Further, a longitudinal length of each sensor is assumed to be “d”. FIG. 8 is a diagram illustrating an example of a worst case on the discrimination (hereinafter, separation) of two objects in the touch panel. In the sensor 10 illustrated in FIG. 8, if the sensor A 801/sensor B 802/sensor C 803 are disposed from above and the sensor D 804 is disposed at a lowermost portion, the multi-touch in which the two objects are touched to four sensors 10 is made. The “touch 1” is in a state in which the sensor A and the sensor B are each touched at an area share of 50% and the “touch 2” is also in a state in which the sensor C and the sensor D are each touched at an area share of 50%.
Therefore, the amplitudes of the touch signals detected in each area are the same, which is a case (case 1) 810 in which the separation is impossible since the amplitudes of the signals are the same when looking at the amplitudes of the signals displayed at a center of FIG. 8. A distance between the respective central points of the touch 1 and the touch 2 is 2d, when an interval between the objects is larger than 2d (distance between the respective central points), the touch area of the sensor A or the sensor D is increased and the touch area of the sensor B or the sensor C is reduced and therefore two vertexes are detected like the amplitudes of the touch signals illustrated in the right of FIG. 8, such that the separation may be made (case 2) 820.
As illustrated in FIG. 6, the form in which the sensors 10 are regularly disposed at up, down, left, and right sides is called a stripe structure (hereinafter, stripe). The interval between the sensors 10 required for the separation of the objects in a column direction or a row direction in the stripe structure is 2d in the embodiment of FIG. 8. The interval between the sensors 10 required for the separation of the objects is 2d, and therefore the number of sensors 10 (since a basic length of the sensors needs to be reduced) required to maintain the interval between the sensors for the separation at 1d or 1.5d is increased, such that the touch IC 30 may be increased and prices may be increased.